In order to convert formats or image sizes, it is required to acquire pixel data having a phase different from a phase of pixel data of an input image signal so as to obtain an output image signal therefrom. In this case, the format or the image size thus converted makes a phase relationship of the pixel of the output image signal to the pixel of the input image signal univocally determined.
As an example of a format conversion, description will be made as to a case where an input image signal is a 525i signal and an output image signal is a 1080i signal. The 525i signal means an image signal in an interlace system consisting of 525 lines. The 1080i signal means an image signal in an interlace system consisting of 1080 lines. FIG. 16 shows a positional relationship between the pixels of the 525i signal and the pixels of the 1080i signal. Herein, large dots are pixels of the 525i signal, and small dots are pixels of the 1080i signal. Solid lines express the positions of pixels in odd fields and broken lines express the positions of pixels in even fields.
When converting the 525i signal into the 1080i signal, it is required to obtain a pixel block in the unit of 9×9 of the 1080i signal in correspondence with each pixel block in the unit of 4×4 of the 525i signal in the respective odd and even fields.
FIG. 17 shows a phase relationship in a vertical direction between the pixels of the 525i signal and the pixels of the 1080i signal. In FIG. 17, the numerical value assigned to each pixel (indicated as a smaller circle) of the 1080i signal means a shortest distance from the pixel (indicated as a larger circle) of the 525i signal in a vertical direction. In this case, the interval between the pixels of the 525i signal in a vertical direction is set to 16. In this FIG. 17, each of the numerical values assigned to each pixel of the 1080i signal shows phase information of this pixel in a vertical direction with respect to the pixel of the 525i signal.
The phase information is set to a negative value when the pixel of the 1080i signal is located at a position upper than the pixel of the 525i signal (i.e. a pixel located at the shortest distance from this pixel of the 1080i signal), while it is set to a positive value when the pixel of the 1080i signal is located at a position lower than the pixel of the 525i signal. The same thing is applied to the drawing showing a phase relationship in a vertical direction between an extended graphics array (XGA) signal and the 525i signal, which will be described later.
FIG. 18 shows a phase relationship in a horizontal direction between the pixels of the 525i signal and the pixels of the 1080i signal. In FIG. 18, the numerical value assigned to each pixel (indicated as a smaller circle) of the 1080i signal means a shortest distance from the pixel (indicated as a larger circle) of the 525i signal in a horizontal direction. In this case, the interval between the pixels of the 525i signal in a horizontal direction is set to 8. In this FIG. 18, each of the numerical values assigned to the pixel of the 1080i signal shows phase information of this pixel in a horizontal direction with respect to the pixel of the 525i signal.
The phase information is set to a negative value when the pixel of the 1080i signal is located at a position more left to the pixel of the 525i signal (i.e. a pixel located at the shortest distance from this pixel of the 1080i signal) while it is set to a positive value when the pixel of the 1080i signal is at a position more right to the pixel of the 525i signal. The same thing is applied to the drawing showing a phase relationship in a horizontal direction between the XGA signal and the 525i signal, which will be described later.
Next, as an example of a format conversion, description will be made as to a case where an input image signal is a 525i signal and an output image signal is an XGA signal. The XGA signal is an image signal in a progressive system (i.e. non-interlace system) available at a display with a resolution of 1024×768 dots. FIG. 19 shows a positional relationship between the pixels of the 525i signal and the pixels of the XGA signal. Herein, large dots are pixels of the 525i signal, and small dots are pixels of the XGA signal. In addition, as to the 525i signal, solid lines express the positions of pixels in odd fields and broken lines express the positions of pixels in even fields.
When converting the 525i signal into the XGA signal, it is required to obtain a 8×16 pixel block of the 1080i signal in correspondence with each 5×5 pixel block of the 525i signal in the respective odd and even fields.
FIG. 20 shows a phase relationship in a vertical direction between the pixels of the 525i signal and the pixels of the XGA signal. In FIG. 20, each of the numerical values assigned to the pixels of the XGA signal means a shortest distance from the pixel of the 525i signal in a vertical direction. In this case, the interval between the pixels of the 525i signal in a vertical direction is set to 16. In this manner, each of the numerical values assigned to the pixels of the XGA signal shows phase information of this pixel in a vertical direction with respect to the pixel of the 525i signal.
FIG. 21 shows a phase relationship in a horizontal direction between the pixels of the 525i signal and the pixels of the XGA signal. In FIG. 21, each of the numerical values assigned to the pixels of the XGA signal means a shortest distance from the pixel of the 525i signal in a horizontal direction. In this case, the interval between the pixels of the 525i signal in a horizontal direction is set to 8. In this manner, each of the numerical values assigned to the pixels of the XGA signal shows phase information of this pixel in a horizontal direction with respect to the pixel of the 525i signal.
Although an example of image size conversion is not specifically shown, the phase relationship of the pixels of the output image signal to the pixels of the input image signal is uniquely determined, as is the case of the format conversion described above. For example, in the case where the size of an image (magnification of a displayed image) is magnified by 9/4 times in both vertical and horizontal directions, the same phase relationship is obtained as the phase relationship between the 525i signal and the 1080i signal described above.
Conventionally, it has been suggested to employ the following method at the time when pixel data of an output image signal is to be obtained from pixel data of an input image signal in order to convert formats or image sizes. That is, coefficient data of an estimated equation corresponding to each phase of the pixel of the output image signal with respect to the pixel of the input image signal is stored in a memory. Then, by use of thus-obtained coefficient data, pixel data of the output image signal is obtained by the estimated equation.
As described above, if the format or the image size is different between before and after the conversion, then the phase relationship of the pixels of the output image signal to the pixels of the input image signal becomes different between before and after conversion accordingly. For this reason, if the coefficient data in estimated equation is to be stored in the memory when converting format or image size into various ones, it is required to store the coefficient data therein corresponding to each format or image size in the memory. Further, if image quality is adaptable for many steps when conversions into various formats or sizes are performed, it is required to store coefficient data into the memory in correspondence with each step. In such a case, therefore, it is required to install a memory capable of storing a large amount of coefficient data. This causes inconvenience that the conversion apparatus becomes expensive, and the like.